Question

Which of the following can be used as an acid-base indicator in the laboratory?

• A. White paper
• B. Carbon powder
• C. Liquid blue
• D. Litmus paper

Answer 1

The correct option is D

Litmus paper

Indicators are substances that help us to distinguish between acids and alkalis through colour change. Substances which does not show any colour change in acidic or alkali solution cannot be used as an indicator. White paper remains white in acidic and alkali solution. Carbon-powder remains black in acidic and alkali solution. Liquid blue remains blue in acidic and alkali solution. Blue litmus paper remains blue in colour in alkali solution but changes to red in acidic solution. Therefore, only blue litmus paper can be used as an acid-base indicator in the laboratory.